Image sensors are integrated circuit devices that include a plurality of sensor elements or pixels formed in a semiconductor substrate. The sensor elements are used for sensing a volume of exposed light projected towards the semiconductor substrate. For image sensors, a desire exists to advance quantum efficiency (QE) when pixel size is shrunk down. QE refers to the response with which the image sensor converts light to electrons within each pixel. Various techniques are used to improve QE and sensitivity, including thinning down backside thickness of the substrate. However, when the backend thickness of the substrate is thinned down for optical light path reduction, crosstalk becomes an issue. The optical performance of the sensor is also limited by dielectric film scheme and metal thickness.